OSLO — Norway’s supreme court on Wednesday definitively rejected an appeal by the gunman who killed 77 people in twin attacks last July against a decision that he should undergo a new psychiatric examination.

Norway’s highest court rejected arguments made by right-wing extremist Anders Behring Breivik’s lawyers that the lower Oslo court was not entitled to call for a second psychiatric expert opinion, since it had not been requested by the prosecution or the defense.

Late last year, a first psychiatric probe of the 33-year-old confessed killer found him criminally insane, but the finding was controversial and the Oslo district court last month ordered a second opinion.

Following the supreme court ruling, the two new court-appointed experts will be able to begin observing Breivik.

Although he cooperated with the first examination, he has refused to cooperate with the second team of experts, but the Oslo court ruled last week he should be placed under forced observation to help determine his mental state.

The experts are set to deliver their conclusion by April 10, less than a week before Breivik’s trial is scheduled to start on April 16.

If the first findings are confirmed, the man behind the worst massacre in Norway since World War II will most likely be sentenced to a closed psychiatric ward and not prison.

But regardless of the second expert conclusion on his criminal accountability, he will be tried in court and it will be up to the judge to determine whether he can be sentenced to prison.

On July 22, the man who has claimed to be on a crusade against multiculturalism and the “Muslim invasion” of Europe set off a car bomb outside government buildings in Oslo, killing eight people.

He then went to Utoya island northwest of Oslo, and, dressed as a police officer, spent more than an hour methodically shooting and killing another 69 people, mainly teens, attending a summer camp hosted by the ruling Labour Party’s youth wing.